Gas generator for enhancing propellant ignition



United States Patent 7 Claims Int. Cl. F02g 3/00; F02c 7/26 ABSTRACT OF THE DISCLOSURE A hypergolic gas generator incorporating a catalyst positioned in its combustion chamber for decomposing a hydrazine-type fuel after it has been impinged with an oxidizer so as to minimize residual fuel that tends to cause erratic combustion and lagging ignition. The catalyst is positioned slightly downstream from the point where the propellants are impinged.

This invention relates to gas generators.

In particular, this invention relates to a method and structure for enhancing ignition to prevent destructive detonations and rough combustion.

There are many types of gas generators, examples being rocket engines and the like. Other types include thrust generators for turbines. In any event, this invention is intended for use in any device for producing gas for thrust or power. These gas generators may produce gas by the decomposition of mono-propellants or bi-propellants through the use of a catalyst. Other ways of igniting propellants include the common spark plug of pyrotechnic igniters.

In certain cases bi-propellants will undergo spontaneous combustion. The propellants in such cases are termed hypergolic. Hypergolic ignition, therefore, can be described as a spontaneous combustion which occurs when two propellants come in contact with each other without the need for an igniter or a catalyst.

Examples of hypergolic fuels are hydrazine and hydrazine derivative fuels. These fuels include N H (hydrazine), unsymmetrical dimethyl hydrazine (UDMH), and a mixture of N H and UDMH, typically a 1:1 ratio. A fourth hydrazine derivative fuel is mono-methyl hydrazine (MMH). Also, these fuels may be mixed where desired. A typical oxidizer commonly used with these fuels is nitrogen tetroxide (NTO). When NTO comes into contact with the aforementioned hydrazine derivative fuels, spontaneous ignition occurs, which, as previously described, is hypergolic. Other oxidizers include nitric acid, chlorine-trifluoride and other interhalogen oxidizers. N F is still another oxidizer.

Problems have occurred, however, with hypergolic ignition with the hydrazine derivative fuels and an oxidizer such as NTO. One of these problems occurs when the fuel and oxidizer is first admitted int-o the combustion chamber. A portion of the fuel is not burned resulting in raw fuel accumulation. This accumulation later undergoes combustion resulting in a detonation. When this detontaion provides a pressure greater than double the steady-state design chamber pressure under normal operation, a pressure spike occurs. A pressure spike is arbitrarily set at double the design chamber pressure. When this occurs, it can create dangerous conditions resulting in destruction of the gas generator, cracking of the nozzle wall or similar deleterious effects. Another problem with these hypergolic fuels and oxidizers is combustion instability. This combustion instability takes the form of buzzing which is a very rapid variation in pressure. This is harmful in that variations in thrust occur and vibrations are created which can be destructive.

The instant invention obviates the aforementioned problems. The invention comprises a gas generator utilizing hypergolic propellants which are injected into the combustion chamber and exposed to a catalyst. This catalyst decomposes a part of the unburned fuel to provide a nearly instantaneous source for propagation of ignition without raw fuel accumulation. This catalyst operates not to ignite the two propellants but to decompose a portion of the fuel to aid in ignition. Thus, the instant invention is directed to ignition enhancement rather than ignition per se.

The objects and advantages of this invention will become apparent as this description proceeds taken in conjunction with the drawing in which:

FIG. 1 is a view of a gas generator, a portion of which is in cross-section looking toward the nozzle exit as viewed along line 11 of FIG. 7,

FIG. 2 is a cross-sectional view of the injector splash plate and catalyst assembly as viewed along lines 22 of FIG. 1,

FIG. 3 is a graph of combustion chamber pressure versus time of a typical firing of an engine using hypergolic propellants without the use of a catalyst,

FIG. 4 is a graph similar to that of FIG. 3 but with a catalyst used for ignition enhancement,

FIG. 5 is a graph of combustion chamber pressure versus a more extended period of time of an engine steady state firing without ignition enhancement and is illustrative of combustion instability,

FIG. 6 is a view similar to that of FIG. 5 but is illustrative of an engine firing with ignition enhancement and illustrates the reduction in combustion instability, and,

FIG. 7 illustrates a gas generator such as a rocket engine which can utilize the features of this invention.

Referring to FIG. 7, there is shown a conventional gas generator 2 which in the form shown includes a diverging nozzle section 4, a throat portion 6, a combustion chamber 8 and an injector 10. This generator or engine is conventional with the exception of the ignition enhancement device as more clearly brought out in FIG. 1 and FIG. 2.

FIG. 1 is a view as viewed along the lines of 1-1 of FIG. 7 with portions broken away to illustrate different components of the injection system. Manifold divider 12 is provided so that fuel on one side thereof and oxidizer on the other side thereof are separated in manifold areas 14 and 16 respectively (FIG. 2). Orifices 18 allow the oxidizer to be injected in a stream 20 as more clearly shown in FIG. 2. Fuel in manifold 14 is introduced through orifices 22 in a stream 24 so as to impinge against the oxidizer stream at point 26.

Below the injector face is a plate 28 having an annular lip 30 formed thereon in which are placed a plurality of catalyst pellets 32. The upper face 34 of these catalysts is located slightly below the impingement point 26 of the propellant streams. To seal plate 28 from injector plate 36, an annular O ring 38 is provided. While individual pellets are shown, it is within the scope of this invention to provide other arrangements of catalyst orientation such as an annular ring or surface coating.

In operation, fuel introduced from a source (not shown) into manifold 14 will pass out apertures 22 with oxidizer supplied by another source (not shown) to manifold 16 and will pass out orifices 18. The fuel and oxidizer will impinge at point 26 slightly above the individual catalyst pellets 32.

While ignition is hypergolic and means are not needed to initiate combustion, the catalyst pellets are provided since it has been discovered by applicants that pressure spikes and combustion instability are obviated by the use of the catalysts.

Typical catalysts for this invention include the MFSA and MFSS catalysts manufactured by Englehard Industries. These catalysts comprise an alumina base with platinum, rhodium and lead deposited thereon. The catalyst comes in either the shape of porous spheres or pellets. A spectrographic analysis of the MFSA catalyst by composition and weight percent is as follows; Al23; Si0.-096; Pt--0.13; Rh-0.14; Natrace; Ca--.O0l; Pb--0.13.

The difference between the sum total percentage shown and 100, represent the amount of oxygen and trace impurities contained within the catalyst. This oxygen exists in the form of metal oxides (e.g., A1 0 Si0 rather than Al or Si).

The MFSA catalyst surface characteristics are as follows; active constituents-Pt-Rh-Pb; surface area, m. gm.460; pore volume, ml./gm.0.58; average pore diameter, A.-50.

The MFSS catalyst differs from the MFSA catalyst primarily in the amount of silicon, the percentage of silicon in the MFSS catalyst being approximately four times that of the MFSA catalyst.

Other catalysts include the 405 catalyst manufactured by the Shell Development Company. This catalyst utilizes a noble metal. Still another catalyst comprises urania (U0 This is depleted uranium dioxide which is a biproduct of reactors and is non-radioactive. The catalyst is available from Nuclear Fuel Services, Inc. Other catalysts include the noble metals, e.g. platinum, rhodium, etc., with the above given only as specific examples.

While the principle of operation and the reasons for the reduction in pressure spikes and enhancement of combustion stability are not known, it is believed that the presence of the catalyst initiates a pre-decomposition of the hydrazine derivative fuels which aid in propagation of combustion while at the same time preventing the accumulation of raw fuel downstream of the injector.

Shown in FIG. 3 is a graph of combustion chamber pressure as plotted against time measured from the initial injection of propellants. The total time represented on the graph is approximately 2 milliseconds while the increments of pressure range from 0 to 1400 p.s.i.a. Without the use of a catalyst, it can be seen that a pressure spike 40 is evident which is many times the average duration of pressure which is in the neighborhood of 250 p.s.i.a. It is noted further that the fluctuations of pressure are wide as viewed even after the initial pressure spike 40.

In comparison, FIG. 4 is illustrative of another test utilizing the same propellants, mixture ratio, oxidizer lead (oxidizer lead is the introduction of oxidizer prior to fuel). In this case, however, a catalyst is used in the manner shown in FIG. 1 and FIG. 2 with the result that no pressure spikes occurred and that combustion was relatively smooth and stable throughout the starting period up to 2 milliseconds.

During the testing represented by the graphs of FIGS. 36, the oxidizer lead and other variables were kept constant which through previous experience with other tests were deemed to be the worst conditions for pressure spikes and combustion instability. Thus, it has been determined that pressure spikes occur without the use of a catalyst under these conditions approximately 100 percent of the time while with a catalyst this did not occur.

FIG. 5 is a graph of pressure versus time over a wider range of time approximating 50 milliseconds after steady state firing. A relatively wide band of pressure can be viewed by the lines 46 and 48. This was a test run without the use of catalysts. In contrast, the combustion chamber pressure fluctuations using the catalyst was much narrower as viewed in FIG. 6 since the distance between lines 50 and 52 is much less on the average than that of FIG. 5.

Thus it can be seen that by this invention the problems of transient pressure spikes which occur during starting periods of gas generating devices using hypergolic propellants are obviated. Furthermore, combustion stability is improved during the test of the engine firing.

Having described this invention, it is to be understood that it is to be limited only by the scope of the claims appended hereto.

We claim:

1. In a gas generating device having a combustion chamber and an injector, that improvement which comprises;

means to inject hypergolic fuel comprising compounds selected from the group consisting of hydrazine and hydrazine derivatives and oxidizer in impinging relationship to each other in a combustion chamber,

a solid catalyst in said combustion chamber adapted to partially decompose said fuel,

whereby ignition of said fuel and oxidizer is enhanced.

2. A gas generating device according to claim 1 wherein said fuel comprises a compound selected from the group consisting of hydrazine, unsymmetrical dirnethyl hydrazine and monomethyl hydrazine.

3. A gas generating device according to claim 1 wherein one of said propellants comprises a fuel selected from the group consisting of hydrazine, unsymmetrical dirnethyl hydrazine and monomethyl hydrazine and said oxidizer comprises nitrogen tetroxide.

4. A gas generating device according to claim 2 wherein said catalyst comprises a compound, selected from the group consisting of noble metals and urania.

5. A gas generator comprising means to inject hypergolic fuel and oxidizer in impinging relationship to each other in a combustion chamber, a catalyst in said combustion chamber adapted to partially decompose one of said propellants, whereby ignition is enhanced and further comprising an annular ring extending from said injector downwardly into said combustion chamber, said ring having an inwardly directed splash plate, said splash plate having said solid catalyst thereon with an upwardly directed face, said face being located slightly below the impingement point of said fuel and oxidizer.

6. A method for enhancing ignition of hypergolic propellants comprising oxidizers and fuels selected from the group consisting of hydrazine and hydrazine derivatives in a gas generating device which comprises;

injecting said propellants into a combustion chamber of a gas generating device,

exposing said propellants to a solid catalyst disposed in said chamber, said catalyst being adapted to decompose a portion of said fuel,

whereby ignition of said propellants is enhanced.

7. A method according to claim 6 wherein said oxi dizers comprise nitrogen tetroxide.

References Cited UNITED STATES PATENTS 3,213,610 4/1962 Grigger et al. 60213 2,949,006 8/ 1960 Halliday 60212 2,993,334 7/1961 Burton 60-212 2,994,191 8/1961 Hamilton 60212 X 3,074,231 1/1963 Klein 60--258 X 3,136,125 6/1964 Toone et al 6039.82 3,221,494 12/1965 Chu 14936 X CARLTON R. CROYLE, Primary Examiner.

US. Cl. X.R. 

